1. Field of the Invention
The invention relates to novel glycolate diesters of dithiophosphoric acids, their salts, and to oil compositions containing such salts.
2. Description of the Prior Art
It is known to add compounds to oils in order to improve the load-bearing properties, e.g., extreme pressure and/or anti-wear properties thereof.
One class of such compounds are the metal salts of dihydrocarbyl dithiophosphoric acids, e.g., the zinc salts thereof, which are well known as load-bearing additives for lubricating oils. Such salts may be represented by the formula: ##STR1## wherein: R is the same or different optionally substituted hydrocarbyl group;
M is a metal; and PA1 n corresponds to the valence of the metal M.
Many types of additives have been proposed, e.g., those in which the optionally substituted hydrocarbyl groups represented by R are the same or different alkyl, cycloalkyl, aryl groups, e.g., see U.S. Pat. Nos. 2,410,642, 2,540,084; and 4,212,751, U.K. Pat. Nos. 723,133 and 852,365, as well as groups derived from alkoxylated alcohols and monoester alcohols, e.g., see U.K. Pat. No. 2,070,054 and U.S. Pat. Nos. 3,102,096 and 4,288,335.
Oil compositions containing the metal glycolate diesters of dithiophosphoric acid of this invention show improved extreme pressure and anti-wear properties as evidenced by valve train wear performance as compared to oil compositions containing the prior art metal dialkyl esters of dithiophosphoric acid.